>> Also it is a 4GB drive but with only 3.72GB capacity.Where's the 280MB gone?
Traditionally, capacities were measured in powers of 2, e.g. 1, 2, 4, 8, 16, 32, 64, 128 etc. Because of the way computer architecture works, these were natural boundaries for memory etc in computers. The old 8 bit computers like the Spectrum and the BBC were limited to 64KB of addressable memory space - this was 65,536 bytes (216).
So over time, 1 Kilobyte has become known as 1,024 bytes, rather than 1,000. Similarly, 1 Megabyte = 1,024 KB, or 1,048,576 bytes. Similar for 1GB.
It seems that storage manufacturers use the decimal versions of GB rather than the binary versions... so given you've bought this 4GB storage card ... they use 4GB = 4,000,000,000 bytes... divide this by 1,073,741,824 (230 - the number of bytes in 1 computer GB!) gives you 3.72529 GB